The overall aim of this Program Project is to provide a mechanistic understanding of how different mutations in the genes encoding several cartilage specific macromolecules such as type II procollagen, type IX procollagen and cartilage oligomeric matrix protein (COMP) result in the clinical phenotypes of chondrodysplasia and premature osteoarthritis, and to gain a detailed understanding of the effects of these mutations on the structure and biochemistry of cartilage matrix and on the process of chondrogenic differentiation. In addition, the Program Project will examine the role of novel genes expressed in cartilage which were identified employing differential gene expression profiling on the functions of articular cartilage. The work proposed is a logical extension of the research completed during the previous years of funding. Project 1 will extend the previous identification of COMP mutations in patients with multiple ephyseal dysplasia and pseudo achondroplasia to examine the mechanisms by which these mutations alter chondrogenesis and cartilage differentiation. The proposed studies will employ gene replacement (knock-in) technology in mice and retroviral gene transfer in vitro to determine the mechanisms whereby the mutations cause the clinical phenotype. Project 2 will examine the mechanisms by which different mutations in COL2AI and in COL9A2 result in specific phenotypes and will determine the effects of the mutations on collagen supramolecular assembly and structure by analyzing in vitro fibril formation employing electron microscopy and atomic force microscopy. The find Project will take advantage of previous gene expression profiling results which identified several novel genes expressed in human chondrocytes to unravel their function within cartilage. We expect that the results of this multi-faceted approach will provide a greater understanding of the role that mutations in genes encoding extracellular matrix cartilage proteins play on the pathogenesis of hereditary osteoarthritis and other related diseases. We also expect that the results will have broader implications towards the understanding of the pathogenic mechanisms of non-heritable forms of OA and will also provide novel information regarding the biology of chondrogenesis and chondrocyte function.